The invention relates to a yarn guide for the traversing feeding of yarn to a rotatingly driven winding bobbin for producing a cheese in a winding head of a textile machine.
For the creation of textile bobbins it is necessary in principle to cause the bobbin to rotate, for one, and furthermore to traverse the yarn running up on the rotating bobbin along the bobbin axis. If the yarn is traversed very slowly, a bobbin with largely parallel windings is created. If such a bobbin is to have a larger volume and flat front faces, which are essentially arranged at right angles in respect to the bobbin axis, limiting flanges are required on both sides of the winding. These limiting flanges can be omitted if the yarn traverses so rapidly that crosswise winding results. High winding speeds then also demand a very high traversing rate.
Driving means oriented parallel in respect to the bobbin axis, for example belts, can be employed for this EP 0 311 827 A2 describes such a yarn guide, wherein the belt is driven by means of a step motor controlled by a microprocessor. By means of this it is possible to achieve high traversing speeds, and the yarn guide can be controlled relatively precisely.
A yarn guide, which is roughly assigned to the category of belt yarn guides, is also described in EP 0 453 622 B 1, which can generate the most diverse winding patterns by means of an appropriately controlled step motor, or also an electronically commutated disk-armature motor. Here, the motor is coupled to a driving wheel, around which a string, which carries a yarn guide support for the yarn guide, has been wound several times. A gear wheel is arranged on the same shaft, which meshes with two gear wheels arranged on both sides. In turn, these two gear wheels are fastened on torsion bars, each of which is prestressed in such a way that they are deflected in respect to their equilibrium position during the entire traversing interval of the yarn guide. It is intended by this to avoid load changes, which could lead to damage to the gear drive, particularly at high traversing speeds.
It is intended by the use of the torsion bars to make possible the large angular acceleration required in the area of the reversing points of the yarn guide. Couplings are provided for increasing this effect, which are intended to fix the torsion bars in place near the gear drive prior to the reversing points being reached, in order to achieve with this a shortening of the effective length of the torsion bars together with an abrupt change of the spring constant. For one, this construction makes great demands on the mechanical portions of the coupling, and the gear drive is furthermore not inconsiderably stressed. As a whole, the yarn guide, its yarn guide support, which is displaceable in a sliding rail, the string moving the yarn guide, reversing rollers for this string and the gear drive add to the inertia of the entire system, which has negative effects in particular at the reversing points of the traversed area.
So-called reversing thread rollers which, in connection with rapidly running bobbin winding machines, often effect the circumferential drive for the cheese simultaneously, are widely used for creating the traversing motion. However, here the same displacement angle always prevails, regardless of the fullness of the bobbin, wherein so-called winding patterns are created at defined number of revolution ratios between the bobbin and the drive roller, which lead to considerable problems in the course of subsequent unwinding. For this reason a multitude of so-called pattern disruption methods are described by the prior art.
For being able to create a predetermined winding pattern, for example a precision winding or a stepped precision winding, the drive of the bobbin must therefore be separated from the yarn guide. Inter alia, this is possible by arranging the already mentioned reversing thread roller at a distance from the winding bobbin and to drive it separately. As a rule, a yarn guide then slides in the reversing thread groove. Because of inertia, this system also suffers from disadvantages.
So-called finger yarn guides have been known for a long time (for example, DE-AS 11 31 575, DE-OS 15 60 360), wherein a yarn guide finger is pivotable around an axis which is arranged essentially vertically in respect to the winding bobbin axis. With this finger yarn guide, the transfer of the oscillating motion also takes place interlockingly by means of a cam disk, either directly to the finger yarn guide, as in DE-OS 15 60 360, or via a traversing rod, on which a double lever is resiliently suspended, which itself engages the finger-shaped yarn guide, as in DE-OS 11 31 575. The double lever additionally receives a pulse at the reversing points by means of an abutment, which favors the rapid reversal of direction at the edge of the traversing zone. However, in this case the abutment does not lead to considerable noise emissions or to a reduction of the service life of the device, since the invention is used for the creation of flanged bobbins, with which only a very narrow displacement angle is used. The advantage of both finger yarn guides is that the finger itself constitutes the yarn guide, without a sliding piece, which increases inertia, being additionally required here. Nevertheless, these yarn guides are also limited in respect to the flexibility of the yarn traverse.
Electromechanical drive mechanisms in place of the conventional mechanical drive mechanisms for the fingers used as yarn guides described here have been proposed in the meantime, such as indicated, for example, in EP 0 808 791 A2 or EP 0 838 442 A1, which defines the species.
The energy storage devices at the ends of the stroke of the yarn guide described and represented in EP 0 838 442 A1 are intended to assist the movement direction reversal of the yarn guide and therefore to relieve its drive mechanism, as well as to reduce the dwell time at the ends of the stroke. The position of the energy storage devices can be mechanically changed, so that the stroke of the yarn guide can be adjusted in order to avoid arched edges on the cheese, for example.
Because of the relatively jolting braking of the yarn guide when dipping into the respective energy storage device, such energy storage devices lead to a reduction in the service life of the traversing system, or require that it must have sufficient sturdiness so that its mass, and therefore mass inertia, is increased. At traversing frequencies of 30 Hz and more, however, the mass inertia already plays a considerable role in connection with the drive mechanism. Moreover, noise is created when the yarn guide impacts on the energy storage device, which adds up correspondingly because of the customarily long textile machines.
If the drive mechanism of the yarn guide is regulated by a control device, load bounces result in the area where the yarn guide dips into the energy storage device, which impair the regulating quality of the control.
It is therefore the object of the invention to improve the oscillation behavior of the yarn guide.
In accordance with the invention, this object is attained by means of a novel yarn guide for the traversing feeding of a yarn to a rotatingly driven winding bobbin for producing a cheese in a winding head of a textile machine. In accordance with the present invention, the yarn guide is directly connected with at least one mechanical energy storage device which is permanently coupled with the yarn guide during the entire traversing movement for aiding the reversal of the direction of movement. The potential energy of the mechanical energy storage device continuously increases in the direction toward the dead points of the traversed area. As a result, the mechanical energy storage device together with the yarn guide constitute an essentially harmoniously oscillating mechanical system.
The invention is advantageously further developed by the below-described additional features.
The direct connection of the yarn guide with a mechanical energy storage device results in that no indirect transfer of forces is necessary at all. The only mass creating a moment of inertia is constituted by the yarn guide itself. By means of this the dynamics of the system are clearly improved over the prior art. The forces and moments of inertia in the area of the considerable angular accelerations at the reversing points are very small. It is possible to achieve a very rapid reversal of the direction of movement in the area of the end areas of the traversing movement without a considerably energy outlay.
In this connection it should be pointed out that in accordance with the present invention the entire oscillating body consisting of the yarn guide finger, the shaft supporting it, as well as the coil used as drive mechanism and its frame, are called the yarn guide.
It is possible to change the traversing width exclusively by means of the drive mechanism, i.e. by means of control or regulation. No mechanical adjustment at all is required for this if the energy storage device is designed for a maximum yarn guide stroke. Since with an increased stroke the torque required in the area of the reversal of the movement direction is also increased, the greater potential energy of the energy storage device being created in case of an increased stroke is useful. The noise level is lowered by the jolt-free operation of the yarn guide, and its service life is increased. Moreover, the regulating quality of the control is improved and the precise keeping of the traversing width is simplified.
The employment of a torsion spring, in particular a helical spring, is particularly advantageous in connection with the yarn guide of the invention. With an oscillation amplitude of, for example 60 to 70E, applicable here, such a helical spring also has the same progression of the characteristic curve of the spring to the left and right of the zero point. However, two helical springs can also be employed, which can then additionally be used for the electrical current supply for a coil of a drive mechanism of the yarn guide.
If the helical springs have opposite winding directions, the same spring torque progression is achieved in both oscillation directions in every case. However, as already mentioned, this advantage gains importance only if the angle of the deflection of the yarn guide out of the position of rest exceeds a threshold value, because in that case the progression of the characteristic curve of the spring is different during opening and closing of the spring.
While the energy storage device reduces the area under the graph of the drive torque square up to a third of the value which would be necessary without such an energy storage device anyway, setting the resonance frequency of the oscillating system to the upper limit of the required oscillation frequency leads to the support of the oscillating motion, and therefore the relief of the electromechanical drive mechanism, being especially intense during extreme situations.
It is assured by the sturdiness of the arrestment of the energy storage device, that the energy storage device aids the oscillating motion in both directions to the same extent.
There is, of course, also the possibility to make the selection of the springs from the start in such a way, that their characteristic spring curves corresponds as much as possible to the desired oscillation behavior. In this connection it is even desirable that the characteristic spring curve does not extend in a straight line, but instead progressively increases after the reversing point, as already mentioned. The dimensioning of the spring should be selected for optimization in such a way that the integral under the driving torque square becomes the smallest. Because of this, the required power consumption of the drive mechanism for the yarn guide is the lowest.
The flexibility of the oscillation system can be improved still further if, in addition, the suspension of the at least one spring during the oscillation movement of the yarn guide is adjusted in a controlled manner. In a range of a lesser oscillation frequency, for example 5 Hz, the spring assistance in the reversing area of the yarn guide is required not at all or only to a small extent. The energy for bending the spring or, if an additional spring is used, the two springs, must be supplied by the electrical drive mechanism of the yarn guide in the remaining oscillation range outside of the oscillation dead center points, in which no angular acceleration is present. This energy can be reduced in that the suspension of the at least one spring for all practical purposes oscillates synchronously. This means that at very low oscillation frequencies the suspension could also oscillate with the same amplitude. However, in this case the drive mechanism for the suspension must be included when determining the energy balance. It can therefore be advantageous, depending on the actual conditions, to let the suspension oscillate along at the same frequency, but with reduced amplitude. In that case the bending of the spring takes place only in the lower range of the characteristic curve of the spring.
With increasing frequency, the requirement for assisting the movement reversal increases. For this reason a relief of the spring in the area of the reversing points is disadvantageous. The potential spring energy stored in the area of the reversing points can be clearly increased by appropriate phase-shifting between the oscillating movement of the suspension and of the yarn guide. However, in this way merely a far-reaching effect on a fixed frequency would be achieved, which could also be achieved with a stronger spring or a plurality of springs.
But the flexibility of the system offers the possibility of relieving the spring over the larger part of the stroke by an oscillation of the suspension in the same direction, and to clearly increase the spring force only directly prior to reaching the reversing point by swiftly reversing the a oscillating movement of the suspension into the opposite direction.
A xe2x80x9cweak springxe2x80x9d is created in this way over the larger portion of the stroke length, and a very strong spring in the reversing points. This exactly corresponds to the desired assistance of the oscillating movement of the yarn guide. However, in the course of this, the system is not disadvantageously affected by an abrupt introduction of a spring force or adjustment of a spring constant, as in the prior art already discussed. The flexibility regarding the assistance of arbitrary oscillating movements achieved in this way is not suggested by any of the solutions known from the prior art.
The high degree of flexibility of the movement of the yarn guide regarding oscillation frequency, oscillation amplitude and even oscillation progress over the length of a stroke caused by the mechanical oscillation system is additionally supported by the drive system claimed in what follows.
A relatively high magnetic flux density can be achieved within the air gap in accordance with the invention, wherein the losses are low in case of small dimensions of the air gap and sufficient dimensioning of the yokes, which have a low magnetic resistance. The torque required for deflecting the yarn guide is obtained by providing the coil located in the area of the magnetic flux lines with electrical current.
The size of the coil has a close connection with the adaptation to the gap width of the air gap in accordance with the invention, through which magnetic flux lines flow. The distance of the winding strands of the coil passing through the air gap from the pivot axis of the yarn guide affects the size of the torque which can be created by the drive mechanism. This torque is high in relation to the mass moment of inertia of the coil. The remaining portions of the body taking part in the oscillation can be made of a very light material and only need to have the sturdiness required for the occurring forces, so that a low mass moment of inertia results.
The size and direction of the torque is set by controlling, or regulating, the voltage, and therefore the electrical current, in each phase of the movement. This can take place by means of a control device, for example a microprocessor, which controls the current strength and current direction in accordance with a predeterminable program as a function of the angle and the time in such a way, that the respectively desired traversing angle of the yam results from the traversed width, or that the traversed width or the end points of the traverse can be set. The respective angle is detected by means of appropriate sensing devices, keeping of the set value is checked and, if required, the actual value is matched to the set value by regulating it. Known PID controllers can be used for this, while a known infrared photoelectric barrier, which scans markers arranged concentrically in respect to the pivot axis, can be employed for detecting the torque angle.
The air gap, and therefore also all elements for generating the magnetic field, need merely extend over the pivot range of the electrical coil corresponding to the maximally settable traversing stroke of the yam guide. With this, the structural outlay is appropriately limited. Also, only one electrical coil is required, which moves up and down along the appropriately dimensioned slit during oscillation. As mentioned, it is of particular importance that, the further the elements participating in the pivot movement are removed from the pivot point, the smaller the mass must be which they are allowed to have, since in the area of the dead centers of the oscillation of the yam guide it is necessary to provide considerable angular accelerations, and therefore very high torques must be provided with a large mass moment of inertia of the oscillating parts. It is necessary here to take into account that in the course of producing cheeses on bobbin winding machines, oscillation frequencies of the yam guide in the range of up to 30 Hz are necessary.
In contrast to an electronically commutated motor, wherein commutation during the constant effective direction of the drive motor is required, with the present invention a change in the direction of the electrical current directly leads to a reversal of the sign of the driving torque. This in turn simplifies the control of the direct drive of the oscillating yam guide.